The present invention relates to the field of sensors, and, more particularly, to techniques and devices for sensing pressure exerted at points of a flexible and pliable object in different shapes.
There are several applications for a device capable mapping the pressure and of providing images of the map distribution of the pressure exerted onto a certain surface, not plane nor rigid, but flexible and pliable to conform to different shapes. For example, in the field of the so-called xe2x80x9cintelligentxe2x80x9d toys, but more generally in the field of the manufacturing of intelligent robots, an external covering of the puppet or of the robot could advantageously incorporate sensors distributed in a more or less uniform way on the surface of the flexible and pliable covering material, capable of outputting data representative of a picture of the map distribution of the pressure exerted onto the external surface of the pliable covering. The artificial intelligence incorporated in the device or in the robot could then be able, by reading the real-time map distribution of the pressure of distinguishing for example the distribution map of the pressure exerted by a hand of an adult that may press or handle the toy from that produced by the hand of a child, to discriminate whether the action of the hand is a caress or a strong clasp or a stroke.
Another important field of use of such a bidimensional pressure sensor may concern the problem of detecting systematically the pressure or better the distribution map of the pressure acting on the windward and leeward faces of a sail to optimize its trim by acting onto the numerous devices for regulating the shape and the orientation of the sail in function of the apparent wind. To this aim, classic differential pressure sensors formed by capillaries held close to one face and to the other face of the sail have been used but they are able to provide only an indication of the locally sensed pressure at the position of the capillaries.
The problem of sensing the distribution of the pressure over the whole or a significant portion of the sail surface such to provide a distribution map of the pressure field acting onto the sail has not been resolved yet. Even the optimization of the trim of the sail based on the observation and/or the instrumental detection of a laminar or turbulent character of the air flow at different points of the sail surface, suitably equipped with light ribbons fixed as flags onto the sail surface, is not accurate and cannot be readily managed with modern real time data acquisition and elaboration systems.
There are bidimensional capacitive pressure sensors developed primarily for realizing the so called xe2x80x9ctouch padsxe2x80x9d of portable PC that allow the reconstruction of the position of an object weighing onto the surface of the sensor. U.S. Pat. No. 5,374,787 describes a sensor of the position of such an object onto a sensible surface.
Nevertheless, these known devices are realized with manufacturing techniques of printed circuit boards (PCB), according to which a substrate of fiber-glass or of mylar(copyright) is provided with copper orthogonal stripes defined on one or on the other face of the substrate. Notwithstanding that a substrate of mylar or of another dielectric material may be moderately flexible, at least for small deflections, the sensor so constructed remains substantially rigid and not pliable into different geometric shapes because the copper stripes defined onto the substrate""s surface would break.
It is evident that the known devices are unsuitable to dress a toy or a robot, or to be incorporated in a sail or in any other object that must retain flexibility and pliability to conform to different shapes as a fabric.
An object of the present invention is to provide a device for sensing the pressure exerted at different points of a surface of a flexible and pliable object and a bidimensional pressure sensor formed an array of capacitors integrable or applicable to a flexible and pliable object.
These and other objects are met by the present invention in which a bidimensional capacitive pressure sensor includes a plurality of capacitors formed by two mutually orthogonal sets of plates parallel or almost parallel to each other separated, at least in correspondence of the crossing areas between electrodes belonging to one and the other set, by a layer of an elastically compressible dielectric material, having an array or matrix of column plates and row plates separated, at least at crossings, by the elastically compressible dielectric. The system for biasing and reading capacitances comprises circuits for selecting a column and a row plate and a sequential control logic circuitry of the column and row selection circuits for generating read values of the pressure each relative to a single pixels represented by the capacitor realized in the superposition or crossover area of a selected column plate with a selected row plate.
According to a first embodiment, each of the two arrays of parallel electrodes may be realized in the form of a fabric composed of weft oriented threads of a dielectric material and of warp oriented threads alternately of a conducting material and of a dielectric material (or even viceversa). The threads of conducting material of the fabric form the parallel electrodes of a respective array and two fabrics of this kind are firmly fixed onto the opposite faces of a dielectric layer, for example a latex layer or of an elastically compressible expanded plastic material, orienting the fabrics so that the threads of conducting material of one array are orthogonal to the threads of conducting material of the other.
Alternatively, the two arrays of parallel plates or substantially (quasi) parallel plate electrodes or short plates may be realized in the form of parallel stripes of a conducting paint applied onto a respective face of a dielectric layer or multilayer comprising at least a layer of latex or of an elastically compressible expanded plastic material. Still alternatively, the two arrays of electrodes parallel or substantially so may be formed by a plurality of stripes of adhesive tape incorporating a ribbon of a conducting material, set onto the surface of a flexible article or object capable of being draped over objects or of assuming different shapes even not planar when so solicited. The second array of electrodes may be applied onto the first array of electrodes interposing a dielectric pad of an elastically compressible material in each crossing zone between an electrode of the first array and an electrode of the second array.
According to a further embodiment, each dielectric pad of an elastically compressible material may comprise metal caps on both faces that are thus contacted by a ribbon or thread of conducting material that is incorporated in the respective adhesive tape of one array or of the other array. Substantially, in direct and intimate association to a flexible and even pliable article such as a fabric or a multilayer that may even incorporate a layer of an elastically compressible material, an array of capacitors ordered in rows and columns is realized whose electric connection lines are individually selectable such to allow a measure of the capacitance of a single selected capacitor, established by the superpositions on a certain area of intersection of a selected row conductor and of a column conductor.
The whole area of the array or matrix of capacitors on the pliable and flexible object may be analyzed pixel by pixel (measures of single selected pixel capacitances). Independently from the shape momentarily or permanently assumed by the flexible and/or pliable object and thus from the xe2x80x9cstaticxe2x80x9d stresses that may be induced by the plates of the single pixel capacitors to the respective electrical compressible dielectric layer, effects that may be partially or completely filtered out or compensated by the detection circuitry, the scanning of all pixels (capacitors) of the so constituted array may provide a map representation of the distribution of the pressure i.e. of the relative values of the pressure being exerted at each pixel sensing capacitors distributed onto a complex surface of the flexible and/or pliable object.
The plate electrodes, whether in the form of threads of conducting material, woven with threads of a dielectric material to keep them electrically isolated from each other, or thin ribbons of conducting material incorporated in an adhesive tape of a dielectric material or stripes of a conductive paint, are flexible and/or pliable into the different shapes that may be assumed by the fabric or in general by the support material whether in the form of a textile fabric or of another kind and do not cause any substantial stiffening of the flexible and/or pliable object onto which they are applied or are part of.
Appropriate terminal connectors permit the individual connection of each row and of each column plate electrode to as many pins of a selection circuit for selecting a row line and a column line, according to a pre-ordered scanning scheme per single pixels of all capacitors (crossing points), and appropriate biasing and measuring circuits determine the current value of capacitance of each pixel capacitor.
The read circuitry eventually produces a digital data stream relative to pictures of the distribution map of the pressure onto the bidimensional sensor, in terms of relative and/or absolute pressure that are generated in a real time made by the device of the invention, at a certain xe2x80x9cframe frequencyxe2x80x9d.